A riser tensioner is present on all vessels connected to a marine riser. The purpose of the tensioner is basically to carry the weight of the riser and apply additional top tensioning force to the riser as well as absorbing movement between the vessel and the marine riser.
Due to space and cost savings in combination with good technical function, hydraulic riser tensioners are widely used.
Hydraulic riser tensioners employ hydraulic cylinders as their active element. The end portion of the hydraulic cylinder that includes the fluid cylinder part of the hydraulic cylinder is often connected to a support frame, the support frame being fixed to the vessel. The hydraulic cylinders piston rod end portion is often connected to the riser.
The piston rod of the hydraulic cylinder is exposed to the environment when outside the cylinder. It is well known that the piston rod is attacked by chloride ions from the marine environment. In addition grit and other particles coming through the air attaches to the often wet piston rod. The result is corrosion and increased wear of the piston rod, bearings, and seals.
Extensive work has been undertaken in order to develop materials and designs that are able to withstand such harsh working conditions. Although progress has been made, the problem is not solved, and maintenance cost is running higher than acceptable. Therefore, apparatus to overcome or reduce at least one of the disadvantages of the prior art would be welcome by the industry.